The period of chemical history we call alchemy spans about three centuries, roughly AD 1400 to AD 1650. The first chemistry textbook, that of Andreas Libavius (Frankfort, 1597), still bears the title Alchemia. Certainly the high point of traditional Western alchemy is between 1450 and 1650, although isolated individuals are both earlier and later. Alchemy is perhaps best summarized by its greatest practitioner, Paracelsus (AD 1493 --1541). Johann Baptista Van Helmont of Brussels (AD 1579 - 1644), who has been called both the last alchemist and the first chemist, begins the final two centuries of transition (AD 1600 -1800) which lead into an essentially modern chemistry.
The alchemical contribution to chemistry was a mixture of concepts and techniques derived from three sources: the systematic logical approach of the scholastics in the general Christian milieu of the Middle Ages, the knowledge of Arabic medicinal chemists which probably entered Europe through Moorish Spain, and the development of some industrial chemistry during the Middle Ages. This practical chemistry had advanced comparatively little over the ancient world up to AD 1200, and much known to the Greeks and Romans had been temporarily lost, but by AD 1500 many processes were in small-scale use throughout Europe. The metals known were the same as in the ancient world and production was generally on a small scale. The scale of metal production was not all that small; for example, for Richard the Lionhearted's crusade the smiths of the Forest of Dean made 50,000 iron horseshoes. Water-powered hammers and often water-powered furnace bellows were used; industry may have been on a small scale by modern standards, but it was beyond a backyard basis. The practical metallurgical processes used at this time are given by Agricola.
The chemical processes used were simple - heating in furnaces, boiling in pots or cauldrons, distillation, pounding and grinding. Some materials were produced in fairly large quantities: charcoal, prepared from wood, for fuel use; pitch and tar, byproducts of charcoal, for the building of ships; lime, for cement, prepared by heating chalk or limestone; and soap. Soap, which had been made from olive oil or fat treated with soda ash since about 800 AD, was now made of animal fat plus potash which had been treated with lime. Soda ash was little used, and potash (KCl) was leached from wood ashes with water. Glass was well known, and glass vessels had become easier to manufacture since the glassblowing pipe was invented around AD 950. Other materials were known but produced in smaller quantities, such as ammonia by distilling stale urine or the hooves of beasts (which gave it the obsolete name spirits of hartshorn), painting pigments, dyes, and medicinals.
Paracelsus, whose actual name was Philipp Theophrastus of the family of Bombaste von Hohenheim, was born in Einseideln (Switzerland) in 1493, the son of a medical man. His father trained him in mineralogy and chemistry, as well as in medicine, in the Austrian mining area of Carinthia. After initial studies in Basel (Switzerland) in 1509, he probably completed a M.D. at Ferrara (Italy) and in 1527 was appointed Professor of Medicine at Basel. A controversial figure, said to have publicly burned the writings of Galen and Avicenna with sulfur and nitre while wishing the same fate upon their authors, he was unpopular with other medical men and soon left Basel in disgrace. The rest of his life was spent in wandering about Europe, and he died in 1541 in Salzburg (Austria). The poster shown in Figure 1.4 may have been publicity for one of his presentations or books, and is earlier than 1565.
To the Arabic idea that metals were composed of the two principles of mercury and sulfur and were generated slowly in the earth from these, Paracelsus seems to be responsible for adding the principle of salt. The basis of matter was the alchemical trinity of principles-- salt, sulfur and mercury. Salt was the principle of fixity (non-action) and incombustibility; mercury was the principle of fusibility (ability to melt and flow) and volatility; and sulfur was the principle of inflammability.
The idea of the three principles was sometimes used in conjunction with the Aristotelian four-element system by Paracelsus in a way in which to modern readers, and even contemporary readers, is most obscure. It is reported, and accepted by at least one serious historian, that he dictated his works while drunk - which may account for some of the obscurity. We may see how this shows up in the words of Paracelsus himself:
"Now, as to the philosophy of the three prime elements, it must be seen how these flourish in the element of air. Mercury, Sulphur, and Salt are so prepared as the element of air that they constitute the air, and make up that element. Originally the sky is nothing but white Sulphur coagulated with the spirit of Salt and clarified by Mercury, and the hardness of this element is in this pellicle and shell thus formed from it. Then, secondly, from the three primal parts it is changed into two - one part being air and other chaos - in the following way. The Sulphur resolves itself by the spirit of Salt in the Liquor of Mercury, which of itself is a liquid distributed from heaven to earth, and is the albumen of the heaven, and the mid space. It is clear, a chaos, subtle and diaphanous. All density, dryness and all its subtle nature, are resolved, nor is it any longer the same as it was before. Such is the air. The third remnant of the three primals has passed into air, thus; If wood is burnt it passes into smoke. So this passes into air, remains in its air to the end of its elements, and becomes Sulphur, Mercury, and Salt, which are substantially consumed and turned into air, just as the wood which becomes smoke. It is, in fact, nothing but the smoke of the three primal elements of the air. So, then nothing further arises from the element of air beyond what has been mentioned."
Despite alchemical obscurity, the doctrine of the three principles is a definite advance on the doctrine of the four elements. The four elements were ideals and as such unattainable. One could never have pure earth, air, water, or fire, only mixtures of these ideal forms. One can, however, obtain pure principles fairly easily. The idea of purification of substances came in, not surprisingly, through medicinal chemistry. Pure drugs were found to be far less harmful to the patient than impure ones. By the beginning of the sixteenth century (AD 1500) medicinal chemists could and did prepare quite a few pure substances in the comparatively small quantities required for drug use.
The methods used by early medicinal chemists to obtain pure substances from naturally occurring mixtures are still used today. Since the physical properties of different pure substances are different, physical methods can be used to separate a mixture into its component pure substances. When a volcanic rock containing sulfur is heated, the sulfur turns from solid to gas (sublimes) and recondenses as a virtually pure solid on any nearby cool surface; the remainder of the rock remains behind as a solid. Quite pure sulfur can easily be prepared in this way. Mercury, when it is a component of a mixture, turns from liquid to vapor, or distills, from the mixture more readily than any other metal or most metal compounds; it also will recondense as a liquid on an adjacent cool surface. This process of distillation can be used to prepare pure mercury because few of the materials with which mercury is found vaporize at as low a temperature as does mercury. Distillation was then, and still is, extensively employed to prepare pure substances; pure water can be prepared from seawater, for example, because the water is vaporized at much lower temperatures than is salt.
Simple sublimation or distillation is adequate to prepare pure samples of a comparatively small number of substances, all of them volatile. The third member of the alchemical trinity, common salt, cannot be so prepared. Salt was purified by a different method, fractional crystallization. Impure salt, or sea salt, is obtained by evaporation of seawater either in naturally occurring ponds or in man-made enclosures, and has long been an item of commerce. Sea salt consists primarily of common or table salt, sodium chloride, together with smaller amounts of magnesium and calcium salts. When seawater is evaporated, the first crop of crystals to come down are almost pure sodium chloride; most of the other salts remain in solution until almost all of the seawater has evaporated away. If this first crop of crystals is redissolved in pure (fresh) water and then that solution is in turn evaporated, the first crop of crystals to separate as that solution evaporates will be still purer sodium chloride, since the remaining impurities will again tend to remain in the solution. Fractional crystallization is used today, as it was then, in the preparation of pure salt for table use. It is also used in the preparation of other pure salts, but it is limited in effectiveness to those materials in which the impurities are present in comparatively small amounts, such as a few per cent. A 50:50 mixture of two pure substances is not easily separated by fractional crystallization.
An analogous method, fractional distillation, can be used to separate mixtures of liquids. Modern oil refineries are basically rather large and elaborate fractional distillation units with some auxiliary equipment. Fractional distillation seems to have been discovered around 1100 AD by alchemists of the medical variety in Italy and is frequently mentioned from the twelfth century onward. The cleric Arnold Bochmove (Arnold de Villanova, 1235 - 1310) gives recipes for liqueurs based on distilling wine with spices and herbs. Distillation of wine to produce gin and liqueurs became known in Paris by 1332 and spread throughout Europe. Liquors of various types were produced, most of which are still well known, such as brandy (from the Dutch brandewijn, burnt or distilled wine) and schnapps. Regulations to control heavy drunkenness and the unruly behavior of the Schnappsteufeln (schnapps fiends), along with taxation of alcohol, date back to the thirteenth century. Distillation of fermented cereals such as barley and rye to produce "John Barleycorn" originated with the brewers of beer in the fourteenth century; aqua vitae and its attendant problems have troubled individuals and governments ever since.
The cleric Raymond Lully (1235 - 1308?) was the first to prepare pure ethanol, by distilling fermentation alcohol three times from quicklime, CaO. Normal fractional distillation can produce only 95% ethanol (95% C2H5OH - 5% H2O) because ethanol and water mixed in this composition form an azeotrope. An azeotrope is a mixture with a fixed boiling point that cannot be further separated by fractional distillation. The quicklime must be added to remove the water from this azeotrope by chemical reaction: CaO + H2O --> Ca(OH)2.
Another important attribute of medicine was that formal schools of medicine were established very early. The body of medical knowledge, including procedures for the preparation of compounds, was formally taught. Moreover, within the medical profession there was, and is still, a comparatively free flow of information, while in the days of alchemy there were considerable efforts made to conceal possibly valuable knowledge. The alchemists whose writings are informative, such as Paracelsus, his follower Oswald Croll whose Basilica Chymica (Frankfurt, 1609) is a clearer statement of Hermetic-Paracelsian doctrine, and Van Helmont, had all obtained M.D. degrees.
Up until perhaps 1500, alchemy had two objects: the artificial production of gold and the production of an elixir of life which gave life and health to those who drank it. This second goal gradually merged into medicinal chemistry, leaving alchemy with the objective of gold production. In China, alchemy always retained the search for the elixir of life as its major goal and little to no effort was devoted to transmutation of other metals to gold; however, this emphasis had no effect on Western Europe since communication with China was virtually nonexistent. The production of gold was supposed to occur by the treatment of other base metals with the philosopher's stone, also called the red elixir. As a consequence much of the work in alchemy was related to contemporary methods of metallurgy.
The idea of conversion of other metals into gold was not as unreasonable to the alchemists as it appears to a modern chemist. Metals were composed of different amounts of the three principles, especially salt and mercury, and slowly changed in the earth from one metal or metal ore into another spontaneously. The more desirable, and naturally less abundant, metals such as gold formed spontaneously, but only very slowly, probably from iron to copper to lead to silver to gold. Thus the only purpose of treatment was to speed up the process which was already taking place so that gold could be obtained in hours rather than millennia - an idea very similar to the modern industrial practice of catalysis.
Most of the methods of alchemy were the methods used in industrial chemistry at about the same time, especially those of smelting of metal ores, working of metals, glassmaking, and the dyeing of fabrics. There were a few special methods used only in alchemy: use of stills, or alembics; use of stills with reflux, the kerotakis; many different types of furnaces; use of the waterbath (in French, still called the bain-marie, after Mary the Jewess, who is often erroneously associated with Miriam, sister of Moses), the sand bath, and the ash bath. The technique of grinding, as in the mortar and pestle, came from contemporary medical preparation methods. One of the most interesting and unique of these devices was the kerotakis, a tubular metal container.
In a kerotakis, metals like lead or copper could be heated over sulfur and were converted into black sulfides; treatment of materials with mercury was also possible. Mercury was often used as an agent of change because under alchemical treatments dramatic color changes were observed, the metal being silver, the oxide red, and the sulfide black.
The idea that transmutation of metals was possible has a basis in practice as well as in theory. For example, the ore galena (PbS) looks metallic. When heated in the presence of air, it is converted into lead with loss of sulfur dioxide (SO2) as a gas:
PbS(s) + O2(g) --> Pb(l) + SO2(g)
One metal is apparently converted into another. Moreover, solid silver sulfide, Ag2S, normally occurs together with PbS and the silver sulfide is reduced by the same treatment. As a consequence, a silver-rich lead ore will produce a Pb-Ag alloy which looks like lead. On slow heating, the lead is oxidized and removed as the oxide leaving behind the metallic silver, another example of apparent transmutation, now from a large amount of lead to a small amount of real silver. Moreover, iron pyrite (FeS), often called fool's gold, can be reduced to iron metal; when this is done along with lead or its sulfide galena, the iron dissolves in the resulting molten lead. The lead and iron can again be oxidized by heating, and any gold which existed in the pyrite, as gold sometimes does, will remain in the crucible.
There are some less honest ways of apparently converting lead into gold, including outright fakery. For example, one can stir a mixture being heated with a hollow rod containing gold powder and closed at the end with wax; the gold will run out and into the mixture. Or one can make a nail half of gold and half of some other metal, paint it, and dip the nail into something that dissolves the paint. Or, if this is too obvious, one can make the whole nail of the silver-gold alloy electrum. When the nail is dipped in a dilute solution of nitric acid (HNO3), the silver reacts and dissolves out while the gold does not so part of the nail appears to change from silver (the silver color of electrum) to gold. These and other frauds were used by swindlers styling themselves alchemists, such as Giuseppi Balsamo ("Count Cagliostro", AD 1743 -1789?).
There were two major technical problems which held back the advances of alchemy into modern chemistry in addition to its objectives. One of these was difficulty in controlling the degree of heat, since no thermometers had yet been devised, and so alchemists generally had banks of furnaces for every conceivable use. The other difficulty was their failure, like others before them, to consider mass an important property in chemistry, despite the fact that adequate balances had long been in use by jewellers and coiners.
For a list of substances used by various alchemists see An Alchemists Glossary of Terms, Definitions, Formulas & Concoctions.